Even with the most educated of job applicants, there is one skill that can’t be taught in any classroom: customer service.

You can decorate your resume with private colleges and fancy degrees but learning how to interact professionally and courteously with customers, coworkers or just other human beings is something you learn through experience.

Most teens and twentysomethings learn these skills through the jobs that usually come along with being a college student. We wait tables, answer phones, run cash registers, and in some cases, learn as much by doing so as we do on campus.

As a waitress and cashier in my early years, I learned how to treat people. And more importantly, how NOT to treat people. Anyone who’s worked as wait staff or a bartender will tell you that you can learn so much about the human race just by standing on your two feet … usually while smiling through your teeth while someone yells at you.

Another thing you learn in customer service jobs: appreciation. When you’re understaffed and people are impatient and snapping at you to bring them more coffee, you want to hug that one customer that tells you, “I see you’re busy and working hard, take your time,” and tips you well. Those customers make your night. And the reason those good customers exist is because more than likely they have been where you are.

My husband likes to laugh at me when I stack plates and tidy up tables after every restaurant meal, but in the mind of a former waitress, it would be rude not to do so. And for me to tip less than 20 percent, you would probably have to spit in my food right in front of my face. It’s the same idea as returning the shopping cart you use at the grocery store to the cart corral — or better yet — getting some exercise and walking the 20 feet back to the store with it, if you’re able. In my opinion, that’s just being a good human being, even if your rationale is that someone is getting paid to do that task.

As a teenage grocery store cashier, I was once brought to tears by a woman who berated me in front of a line full of people because her credit card was declined. As a an adult, when I witness a customer being rude to a cashier who’s doing their job well, I speak up because I know they can’t — and because I know the person being rude to them doesn’t understand what it’s like to be in that position.

Even as an adult working in a professional office, there are still days when I’m greeted by yelling on the other end of the phone. And when this happens, it’s the years of customer service that thickened my skin helping me help them without losing my cool.

Younger generations who never get to have these interactions don’t experience a big part of what it means to be, frankly, a good human being to other human beings. And they become … not the best customers.

Internships are a starting point for college students in terms of real-world experience, but maybe there’s a chance for students who work and study to earn credits or incentives.

When you’ve got a job applicant sitting in front of you, ask questions outside their professional resume. A person’s life experience can be just as valuable to your business.